Method for extending the effective life of an oxygen scavenger in a container wall

ABSTRACT

A method of filling a container, and thereby extending the effective life of an oxygen scavenger, includes providing a container having an oxygen scavenger material, introducing product contents and a liquefied gas into the container to displace at least a portion of the air within the headspace, and capping or otherwise sealing the container. Displacing oxygen from the headspace diminishes the available oxygen within the container that can permeate into the container sidewall, thereby extending the effective life of the scavenger.

BACKGROUND

[0001] This invention relates to processing and filling containers, andmore particularly to processing and/or filling containers having anoxygen scavenging material.

[0002] Polyethylene terephthalate (“PET”), polypropylene, or otherthermoplastic materials are often employed for forming containers forcomestible products, such as food and beverages—especially beer, juices,and the like. Containers suitable for filling processes at whichelevated temperatures are employed (including for example filling acontainer with a product that is at an elevated temperature,pasteurizing a container after filling, and the like) will be referredto herein as “hot-fillable.” Hot-fillable containers generally are blowmolded and a heat set process during which the containers are subjectedto elevated temperatures for predetermined time periods in order toincrease crystallization and decrease orientation of the polymer. Heatsetting, which increases crystallinity, is beneficial, among otherthings, to reduce shrinkage of the container at elevated temperature.Container configurations, blow molding techniques, and heat settingtechniques for both hot-fillable containers are well known.

[0003] Typically, hot-fillable containers are not designed to withstandpositive internal pressures, but rather such designs focus onmaintaining an appropriate and desirable shape during vacuum deformationupon cooling of the contents after capping. Thus, collapsible ordeformable portions are often formed in the container wall, and thehot-fillable base is typically designed to withstand only negativepressure. U.S. Pat. No. 5,251,424, entitled “Method Of PackagingProducts In Plastic Containers,” which is incorporated herein in itsentirety, describes a method of hot filling a plastic container thatincludes introducing liquid nitrogen into the container prior to cappingfor providing a positive internal pressure. The '424 patent states thatadvantages of such a technique include eliminating vacuum panels,enabling reduction of container thickness, and control of the headspacevolume. Numerous references disclose introducing nitrogen into metalcans prior to application of a can end.

[0004] PET and many other plastics suitable for containers are permeableto oxygen, whether the container is hot-fillable or is suitable foranother filling process. Thus, the shelf life of comestible products inPET or other plastic containers is limited or decreased by oxygenpermeation through the container surfaces, and comestible productspackaged in such containers are subject to spoilage. Pressurizing acontainer formed entirely of PET with liquid nitrogen would likely havelittle effect on product shelf life. Thus, in efforts to reduce oxygenpermeation, an oxygen barrier may be employed. For example, a multilayercontainer may include an outermost and an innermost layer (that is,forming the container chamber surface) of virgin PET, with an oxygenbarrier material, such as EVOH, therebetween. Often, tie layers areemployed between EVOH and PET.

[0005] The commercial acceptance of containers employing conventionalbarrier layers has been limited at least in part because theeffectiveness of the oxygen barrier is less than commercially desired,even if additional coatings or layers are employed. Oxygen scavengingcompounds in a container wall are often employed rather than barrierlayers described above. For example, U.S. Pat. Nos. 5,955,527;5,639,815; 5,049,624; and/or 5,021,515 (which will be referred to as the“Packaging” patents) disclose an oxygen scavenging material that issuitable for use in bottles in hot-fillable and other containers. Oxygenscavenging compounds have a finite effective life (that is, useful life)because eventually the oxidizable material oxidizes to a degree thatenables oxygen to permeate through the container wall (that is, theoxidizable material is essentially used up).

[0006] Thus, there is a need for container technology that extends theeffective life of an oxygen scavenger or the shelf life of a product ina container.

SUMMARY OF THE INVENTION

[0007] In a conventional container that includes an oxygen scavengingmaterial in the container wall, oxygen is available to permeate bothfrom outside the container (that is, from the ambient atmosphere) intothe oxygen scavenging material and from within the container (that is,from the enclosed chamber) into the oxygen scavenging material. Oxygenis typically available from inside the container because it is presentin the container headspace upon capping, and also possibly because it isdissolved in the product. The oxidizable material in the container wallportion surrounding the headspace may have a diminished effective lifecompared with other portions of the container wall because of the oxygenpermeation from both inside and outside the container in circumstancesin which the concentration of oxygen (and/or the mass transfer rate ofthe oxygen into the container wall) is greater in the headspace than inthe product

[0008] Displacing oxygen from within the container headspace prior tocapping diminishes the (molar) quantity and/or partial pressure ofoxygen inside the container, thereby diminishing the amount of oxygenthat is available to permeate from inside the container into thecontainer wall. We have found that displacing some oxygen from theheadspace increases the effective life of the oxygen scavenger in thecontainer wall in the region of the headspace.

[0009] Diminishing the oxygen partial pressure within the container haslittle effect on the gross rate of oxygen permeation from outside thecontainer into the oxidizable material in the container wall, yet itdiminishes the oxygen available within the container for permeating inan outward direction into the oxidizable material of the container wall.Thus, the effective life of the oxidizable material, especially in theportion defining or proximate to the headspace, is extended by thedegree of decrease in oxygen permeation from within the container intothe container wall.

[0010] A method of extending effective life of an oxygen scavengingmaterial disposed in a container wall employs the phenomenon describedabove. The method includes providing a container that has a wallcomprising an oxygen scavenging material. The container wall may beformed either of multiple layers or a monolayer. The multiple layerspreferably include a discrete layer that includes an oxidizable compoundsandwiched between layers that substantially lack oxygen scavengingcapabilities, such as polyethylene terephthalate (“PET”), polypropylene,or other suitable material. The monolayer preferably is a blend of anoxidizable material with a conventional plastic.

[0011] The container is filled with a product and a dose of liquefiedgas up to a fill line, which is spaced apart from the rim of thecontainer to form a headspace. Upon introducing the liquefied gas intothe container, at least a portion of the liquefied gas vaporizes anddisplaces at least a portion of the air in the container headspace. Uponthe displacement of at least some of the air from the headspace, aclosure or liner is applied to the container to seal the container. Theliquefied gas within the container then continues to vaporize to form apositive total pressure within the container. U.S. patent applicationSer. No.______ (Attorney Docket Number CC-3412), entitled “Method ForDiminishing Delamination of A Multilayer Plastic Container,” whichdiscloses related or complimentary technology, is incorporated herein byreference in its entirety.

[0012] In hot-fill applications that would otherwise be subject tovacuum deformation upon cooling of the contents, providing a positivepressure within the container by liquefied gas dosing enables theelimination or diminished size of vacuum panels or other collapsible ordeformable portions of the container, and may also enable alighter-weight container and control over the headspace. Further, thecombination of an oxygen scavenger in the container wall with liquefiedgas dosing is beneficial for product shelf life. In this regard,displacing a portion of the air present in the headspace by introducinga dose of liquefied gas extends the life of the oxygen scavenger in thecontainer wall in the region of the headspace. Extending the effectivelife of the oxygen scavenger, and thus likely extending the productshelf life, applies to hot-filling and non-hot-filling applications.

BRIEF DESCRIPTION OF THE FIGURES

[0013]FIG. 1 is a flow chart illustrating steps according to the presentinvention;

[0014]FIG. 2 is a diagrammatic view of a monolayer container wall;

[0015]FIG. 3 is a diagrammatic view of a three layer container wall;

[0016]FIG. 4 is a view of a portion of a container package with whichthe present invention may be employed; and

[0017]FIG. 5 is a perspective view of the container shown in FIG. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0018] A method of extending the effective life of a container thatincludes an oxygen scavenging material is provided. The presentinvention may be employed with any type of container, including:injection blow-molded bottles, extrusion blow-molded bottles, andbottles formed by any other process; heat set bottles suitable forhot-fillable applications and non-heat set bottles; and jars orcontainers suitable for foods, sauces, and the like.

[0019]FIGS. 4 and 5 illustrate merely one embodiment of a container 9with which the present invention may be employed. Container 9 preferablyis a heat set container capable of withstanding filling with a beverageat hot-fill temperatures, which typically is about 190 degrees F., withvolumetric shrinkage of only a few percent. Heat set processes forforming containers are well known by persons familiar with plasticcontainer manufacturing and design.

[0020] Container 9 is capable of withstanding internal positivepressures contemplated to be encountered in liquefied gas dosingapplications, as well as in pressure filling applications. Theparticular internal pressure rating or design point of a container maybe chosen according to the particular parameters of the application,such as desired internal pressure at a given temperature, carbonizationof the product, container configuration, container wall materialproperties, resistance to abuse, and the like. Such parameters will beunderstood by persons familiar with container design and technology.

[0021] Container 9 includes a base 12, a body 14, a dome 16, a neck 18,and a finish 20. Base 12 preferably has a substantially continuouscontact ring or standing ring on which the container rests. Body 14extends upwardly from base 12, and is preferably substantiallycontinuous. Because the liquefied gas pressurizes container 9, asexplained more fully below, vacuum panels or other features that flexupon internal vacuum are unnecessary. Thus, body 14 preferably issubstantially cylindrical. Body 14 may optionally grip portions. In thisregard, finger indentations 22 may be formed in body 14 to aid gripping.

[0022] Dome 16 extends upwardly from body 14, and yields to neck 18.Preferably, neck 18 is substantially cylindrical or slightly tapered.Preferably, neck 18 is sufficient long to provide an adequate headspacesuch that spilling of the product is unlikely upon initial opening ofthe closure. Finish 20 is disposed at the top of neck 18. Furtherdescription of container 9 is described in co-pending, concurrentlyfiled U.S. patent application Ser. No. ______ , entitled “PressurizableContainer With Contact Ring” (Attorney Docket Number CC-3438), which isincorporated by reference herein in its entirety.

[0023] Container 9 may be formed of any material comprising any oxygenscavenger. The wall of container 9 may be formed in any configuration,including multiple layers or a single layer. In this regard, FIG. 2illustrates a container wall 30 that is formed of a single,substantially uniform composition that includes an oxygen scavenger.FIG. 3 illustrates a container wall formed in multiple layers 32, 34,and 36. Outer and inner layers 32 and 36 preferably are a virgin plasticmaterial, such a polyethylene terephthalate, polypropylene, or othersuitable material. Sandwich between outer and inner layers 32 and 36 isan intermediate layer 34, which preferably includes an oxygen scavenger.The present invention encompasses any combination of layers, includingwalls formed of more than three layers and walls having additionalcoatings.

[0024] Preferably, the oxygen scavenger includes an oxidizable organiccomponent and a metal catalyst for the oxidation of the oxidizableorganic component. The oxidizable organic component preferably is apolymer, such as a polyamide and especially MXD6, which is acondensation polymer of m-xylylenediamine and adipic acid. The metalcatalyst may include cobalt, copper, rhodium compounds and/or othersuitable substances. A suitable material for the oxygen scavenger layeris OXBAR™, which is available from Crown Cork & Seal Company,Philadelphia, Pa. U.S. Pat. Nos. 5,955,527; 5,639,815; 5,049,624; and/or5,021,515, each of which is incorporated by reference in its entirety,disclose technology relating to such a scavenger. The present inventionis not limited to the preferred oxygen scavenger, but rather encompassesemploying any such substance capable of such oxidation.

[0025] Further, particular features or configuration of container 9 areemployed to illustrate an embodiment of a container on which the presentinvention may be employed. The present invention, however, is notlimited to the particular features or configuration of the container.Rather, the invention encompasses a container of any configuration,including without limitation cylindrical and non-cylindrical containers,containers of any dome shape or lacking a dome, containers of any neckconfiguration or lacking a neck, and containers having any standing ringconfiguration, a footed configuration, and the like.

[0026] Referring again to the figures to illustrate the present method,a container, such as container 9, is provided to a filling station forfilling a comestible product, such as juice, sauces, and/or the like.The product is filled up to a predetermined fill line, which isillustrated by reference numeral 24 in FIGS. 4 and 5. Preferably, theproduct is introduced at conventional hot-fill temperatures, such as 180to 190 degrees F. The product may be filled by any type of gravityfilling process in which the product is allowed to flow into container 9under atmospheric conditions or at a low head pressure, a pressurefilling process in which the product is pumped into container such thatthe container encounters a positive internal pressure (typically a fewpounds per square inch), or other filling method.

[0027] A predetermined dose of liquefied gas is introduced intocontainer 9 either just prior to, concurrently with, or afterintroduction of the product into container 9. The liquefied gaspreferably is an inert gas, and even more preferably is liquefiednitrogen. The liquefied gas may be introduced into the container priorto, concurrently with, or after the product in introduced into thecontainer. The product filling system and liquefied gas delivery systemare schematically represented by reference numerals 42 and 44,respectively, in FIG. 5. Equipment and systems for filling plasticcontainers is well known. Similarly, equipment and systems forintroducing liquefied nitrogen or other inert gas into containers,especially metal cans, is well known. Any conventional equipment andsystems may be employed to accomplish such steps.

[0028] Upon filling the container up to fill line 24, a headspace 28 isformed between fill line 24 and the top lip of container 9. The gas inthe headspace upon filling in a conventional process typically has acomposition like that of the atmosphere. In this regard, under gravityfilling conditions, container 9 is essentially open (or at least notsealed air-tight) during the filling process. Similarly, under pressurefilling conditions, the container is open to the atmosphere prior tofilling and prior to capping.

[0029] According to the present invention, the liquefied gas, whichvaporizes upon being introduced into container 9, displaces at leastsome of the oxygen in headspace 28. Closure 26, which isdiagrammatically shown in dashed lines in FIG. 4, is applied to finish20 while at least some of the oxygen is displaced to seal container 9.Similarly, a liner, which may also be represented by reference numeral26, may be applied. Upon application of closure (and/or liner) 26,container 9 is sealed. Because at least some of the oxygen was displacedfrom headspace 28 upon sealing, the composition of the gas in headspace28 includes an elevated partial pressure or concentration of nitrogen(or other gas making up the liquefied gas) and a diminished partialpressure or concentration of oxygen, compared with ambient conditions.

[0030] The diminished oxygen partial pressure within headspace 28provides fewer molecules that may migrate into the container wall 11 or36 compared with an oxygen partial pressure in the headspace ofconventionally filled containers or filling by other means. Similarly,the diminished quantity of available oxygen in the headspace will alsoextend the life of an oxygen scavenger that is formed as part of theliner.

[0031] The present invention encompasses any oxygen partial pressure inthe sealed headspace below ambient (that is, about 3.1 psi) when thecontents reach equilibrium, ambient temperature. Each of the exemplarypressures provided below are the pressure in the headspace immediatelyupon capping, regardless of the headspace gas or product temperature,although it is understood that such pressures will vary upon cooling ofthe product. Vaporization of any liquefied gas in the product aftercapping may increase the total pressure in the headspace. Preferably,the oxygen partial pressure in the sealed headspace is below about 2.75psi, which provides a measurable increase in the effective life of theoxygen scavenger, or even more preferably below about 2.3 psi, even morepreferably below about 1.54 psi, and even more preferably below about0.77 psi.

[0032] The present invention is illustrated with respect to a particularcontainer, although the present invention is not limited to theparticular container configuration or materials described herein.Rather, the present invention encompasses employing any containerconfiguration, container material, or container manufacturing method.Further, the present invention encompasses any filling technique. Eventhough the present invention provides advantages in hot-fillingapplications, the present invention also encompass including filling atany temperature in any type of process. Reference should be made to theclaims to ascertain the scope of the present invention.

We claim:
 1. A method for extending effective life of an oxygenscavenger that is disposed in the wall of a container, comprising thesteps of: a. providing the container formed of a material comprising theoxygen scavenger; b. introducing a comestible product into thecontainer, thereby forming a headspace between a product fill line a rimof the container; c. introducing a quantity of liquefied gas into thecontainer; d. enabling vaporized liquefied gas to displace at least aportion of air in the headspace; and e. capping the container so as tomaintain low oxygen partial pressure within the headspace relative toambient atmospheric pressure, thereby diminishing the amount of oxygenavailable to permeate from inside the container into the oxygenscavenger.
 2. The method of claim 1 wherein the container wall includesan outer layer of PET, an interior layer of an oxygen scavengingcompound comprising nylon, and an inner layer of PET for contacting theproduct.
 3. The method of claim 1 wherein the container wall includes asingle layer comprising a blend of an oxidizable polymer and anon-oxidizable polymer.
 4. The method of claim 1 wherein the containerwall includes a blend of an oxygen scavenger material and polyethyleneterephthalate.
 5. The method of claim 1 wherein the oxygen scavenger isan oxidizable organic component and a metal catalyst.
 6. The method ofclaim 5 wherein the organic component is a polymer.
 7. The method ofclaim 5 wherein the organic component is a polyamide.
 8. The method ofclaim 5 wherein the organic component a condensation polymer ofm-xylylenediamine and adipic acid.
 9. The method of claim 1 wherein theliquefied gas forms a positive total pressure inside the container afterthe capping step (e).
 10. The method of claim 9 wherein the introducingstep (b) includes introducing the comestible product into the containerat an elevated temperature.
 11. The method of claim 10 wherein theoxygen partial pressure within the headspace is below about 3.1 psi. 12.The method of claim 1 wherein the oxygen partial pressure within theheadspace is below about 2.75 psi upon capping.
 13. The method of claim1 wherein the oxygen partial pressure within the headspace is belowabout 2.3 psi upon capping.
 14. The method of claim 1 wherein the oxygenpartial pressure within the headspace is below about 1.54 psi uponcapping.
 15. The method of claim 1 wherein the oxygen partial pressurewithin the headspace is below about 0.77 psi upon capping.
 16. Themethod of claim 1 wherein capping step (e) thereby forms an oxygenpartial pressure gradient across the container wall.
 17. The method ofclaim 1 wherein the quantity of liquefied gas is sufficient to maintaina positive total pressure within the container upon cooling to ambienttemperature.
 18. The method of claim 1 wherein the quantity of liquefiedgas is sufficient to maintain a positive total pressure within thecontainer upon cooling to approximately 50 degrees F.
 19. The method ofclaim 1 wherein the quantity of liquefied gas is sufficient to maintaina positive total pressure within the container upon cooling toapproximately 40 degrees F.
 20. The method of claim 1 wherein thequantity of liquefied gas is such that the container has a substantiallyatmospheric pressure upon cooling to ambient temperature.
 21. The methodof claim 1 wherein the liquefied gas comprises liquefied nitrogen. 22.The method of claim 1 wherein the liquefied gas is an inert gas.
 23. Themethod of claim 1 wherein the liquefied gas is liquefied nitrogen.